In down hole acoustic telemetry systems, signals carrying information are transmitted via compressional waves from the bottom hole assembly (BHA) along a drill string to the Earth's surface. These signals are received by a sensor at the surface, such as an accelerometer. When the drill pipe contacts the borehole wall over more than a nominal area, signal power is lost due to absorption by the surrounding formation. The loss can be especially significant when horizontal wells are drilled, as the contact area can be relatively large.